Bulk Optode Research Articles

Characterization of a new uranyl selective bulk optode; utilizing synergistic effect in optical sensor

A new optical sensor is fabricated for determination of uranyl ion. The optode membrane is prepared by incorporation of 1-(2-pyridylazo)-2-naphtol (PAN), tri-n-octyl phosphine oxide (TOPO) and sodium tetraphenylborate (Na-TPB) to the plasticized poly(vinyl chloride) membrane. In the proposed optode, PAN functions as both ionophore and chromoionophore while TOPO has synergistic effect on the complexation of uranyl ion by PAN. The membrane composition is optimized to yield optimum performance. The linear range of the proposed optode is from 1.00×10−6 up to 1.50×10−4M of UO22+ with a detection limit of 8.20×10−7M. The proposed optode is selective to the uranyl ion in the presence of 1,2-cyclohexylene dinitrilotetraacetic acid (CyDTA). The sensor can be regenerated by exposure to a solution of thiosalicylic acid (0.05M, pH 10) and it was applied to the determination of UO22+ spiked in tap water samples.

Precipitation as a simple and versatile method for preparation of optical nanochemosensors

Optical nanosensors for such important analytes as oxygen, pH, temperature, etc. are manufactured in a simple way via precipitation. Lipophilic indicators are entrapped into nanobeads based on poly(methyl methacrylate), polystyrene, polyurethanes, ethylcellulose, and other polymers. Charged groups greatly facilitate formation of the small beads and increase their stability. Sensing properties of the beads can be tuned by choosing the appropriate indicator. Nanosensors for carbon dioxide and ammonia are found to be cross-sensitive to pH if dispersed in aqueous media. These nanobeads are successfully employed to design bulk optodes. Nanochemosensors with enhanced brightness via light-harvesting and multi-functional magnetic nanosensors also are prepared.

Development a Simple PVC Membrane Bulk Optode for Determination of Lead Ions in Water Samples

A sensitive reversible optical chemical sensor for detecting lead ions is described. The sensor is based on the interaction of Pb(II) with diphenylcarbazone in plasticized PVC membrane incorporating a plasticizer (tributylphosphate). The membranes were cast onto glass substrates and used for the determination of lead ions in aqueous solutions by batch and flow-through methods. When the sensing film came in contact with lead(II) ions at pH 6.0, its color changed from pale orange to pink. Parameters affecting the optode response such as pH, type of plasticizer, plasticizer/PVC ratio, and diphenylcarbazone percent were studied. The optode was found to have a long linear dynamic range, 6 9×10−6 to 1 1×10−2 mol L−1 Pb(II), and a short response time of 180 s with a detection limit of 6 5×10−6 mol L−1 Pb(II) by batch spectrophotometric method. In addition, the sensor has been incorporated into a home-made flow-through cell for determining lead ions in flowing streams with improved sensitivity, precision, and detection limit. In the flow system, the linear calibration range was 1 0×10−6 to 5 0×10−3 mol L−1 Pb(II). The optode could be recovered several times after treating with a 0.005 mol L−1 nitric acid solution. Under the experimental conditions, the response of the optode was fully reversible. The effect of the sample matrices on the determination of Pb(II) was studied. The sensor was used for the determination of Pb(II) ions in river water, tap water, and industrial waste samples with satisfactory results.

A sensitive and selective bulk optode for determination of Hg(II) based on hexathiacyclooctadecane and chromoionophore V

A sensitive new bulk optical sensor (optode) for mercury(II) is described. This optode is based on the interaction of hexathiacyclooctadecane with Hg(II) in plasticized polyvinyl chloride (PVC) membrane incorporating chromoionophore V as lipophilic H +-selective indicator. The membranes were cast onto glass substrates and used for the determination of mercury ions in aqueous solutions. The PVC membrane composition plus the other experimental variables were optimized. With the proposed sensor, mercury(II) can be measured in the range of 2.1 × 10 −7 to 1.2 × 10 −4 mol L −1 with a limit of detection 2.0 × 10 −7 mol L −1 Hg(II). The influence of potential interfering ions on the determination Hg(II) was studied. The sensor showed excellent selectivity for Hg(II) with respect to several common alkali, alkaline earth and transition metal ions. The results obtained for the determination of mercury ions in water samples using the proposed optode was found to be comparable with the well-established furnace atomic absorption method.

Red Light-Excitable Oxygen Sensing Materials Based on Platinum(II) and Palladium(II) Benzoporphyrins

New optical oxygen-sensing materials make use of highly luminescent NIR platinum(II) and palladium(II) complexes with benzoporphyrins. Bulk optodes based on polystyrene and sensing nanobeads based on poly(styrene-block-vinylpyrrolidone) and polysulfone are prepared and characterized. The versatility of the new materials is demonstrated. The features include excellent compatibility with most common excitation sources, high brightness, and suitability for subcutaneous oxygen monitoring.

Ion-Exchange Reaction of Silver(I) and Copper(II) in Optical Sensors Based on Thiaglutaric Diamide

Bulk optode membranes based on a recently reported thiaglutaric diamide ionophore were developed for measurements of silver(I) and copper(II) ions in aqueous solutions. The response properties of optical films containing ionophore and chromoionophores with different pK(a) values were investigated at different sample pH. At certain pH the measuring range of the optode can be shifted when choosing different chromoionophores. Optode with ionophore and chromoionophore V exhibited good responses to silver ions from 10(-6)-10(-1) M at pH 5.5. The proposed sensor showed high selectivity, good reproducibility and stability. With a different chromoionophore ETH 5418 the optode could response to copper(II) ions from 10(-6)-10(-2) M.

Phosphate-selective fluorescent sensing microspheres based on uranyl salophene ionophores

Optical dihydrogen phosphate-selective sensors that function on the basis of bulk optode principles and are based on two different uranyl salophene ionophores are reported here for the first time. The influence of the optode composition and measuring conditions such as sample pH on the optode response are characterized, along with sensor selectivity and long-term stability. Three plasticizers of different polarity are considered for optode fabrication: bis(2-ethylhexyl)sebacate (DOS), dodecyl 2-nitrophenyl ether ( o-NPDDE), o-nitrophenyloctylether ( o-NPOE). The compounds 9-(diethylamino)-5-(octadecanoylimino)-5H-benzo[ a]phenoxazine (ETH 5294, chromoionophore I) and 9-(diethylamino)-5-[(2-octyldecyl)imino]benzo[ a]phenoxazine (ETH 5350, chromoionophore III) are used as H +-selective fluoroionophores that also act as reference ionophores. The resulting optode-based sensors are compared with their ion-selective electrode (ISE) counterparts, and it is revealed that optodes are better suited for operation at physiological pH. The best optode performance was found for the two component optode sensors doped with ETH 5350 and phosphate ionophore(I). The linear range of these sensor was log a = −6.0 to −2.6. Dihydrogen phosphate-selective optode sensors of optimized composition are fabricated in microsphere format and preliminary measurements in diluted sheep blood samples are presented.

Multiplexed Flow Cytometric Sensing of Blood Electrolytes in Physiological Samples Using Fluorescent Bulk Optode Microspheres

Polymeric bulk optode microsphere ion sensors in combination with suspension array technologies such as analytical flow cytometry may become a power tool for measuring electrolytes in physiological samples. In this work, the methodology for the direct measurement of common blood electrolytes in physiological samples using bulk optode microsphere sensors was explored. The simultaneous determination of Na(+), K(+), and Ca(2+) in diluted sheep blood plasma was demonstrated for the first time, using a random suspension array containing three types of mixed microsphere bulk optodes of similar size, fabricated from the same chromoionophore without additional labeling. Sodium ionophore X, potassium ionophore III, and grafted AU-1 in poly(butyl acrylate) were the ionophores used in the bulk optode microsphere ion sensors for Na(+), K(+), and Ca(2+), respectively, in combination with the cation-exchanger NaTFPB (sodium tetrakis-[3,5-bis(trifluoromethyl)phenyl]borate) and the same concentration of the chromoionophore ETH 5294 (9-(di-ethylamino)-5-octadecanoylimino-5H-benzo[a]phen-oxazine) in plasticized poly(vinyl chloride). Excellent reproducibility was achieved for the sensing of potassium ions. The effect of sample pH was relatively small at near-physiological pH and followed theoretical predictions, yet the sample temperature was found to influence the sensor response to a larger extent. Multiplexed ion sensing was achieved by taking advantage of the chemical tunability of the sensor response, adjusting the sensor compositions so that the three types of ion sensors responded with distinct levels of protonation of the chromoionophore. Consequently, three well-resolved peaks were simultaneously observed in the single-channel histogram during the multiplexed calibration as well as in the subsequent measurement of the three cations in 10-fold-diluted sheep plasma. The assigned peak positions corresponded very well to the physiological range of the measured ions.

Polymerized Nile Blue derivatives for plasticizer-free fluorescent ion optode microsphere sensors

Lipophilic H +-selective fluorophores such as Nile Blue derivatives are widely used in ISE-based pH sensors and bulk optodes, and are commonly dissolved in a plasticized matrix such as PVC. Unfortunately, leaching of the active sensing ingredients and plasticizer from the matrix dictates the lifetime of the sensors and hampers their applications in vivo, especially with miniaturized particle based sensors. We find that classical copolymerization of Nile Blue derivatives containing an acrylic side group gives rise to multiple reaction products with different spectral and H +-binding properties, making this approach unsuitable for the development of reliable sensor materials. This limitation was overcome by grafting Nile Blue to a self-plasticized poly( n-butyl acrylate) matrix via an urea or amide linkage between the Nile Blue base structure and the polymer. Optode leaching experiments into methanol confirmed the successful covalent attachment of the two chromoionophores to the polymer matrix. Both polymerized Nile Blue derivatives have satisfactory pH response and appropriate optical properties that are suitable for use in ion-selective electrodes and optodes. Plasticizer-free Na +-selective microsphere sensors using the polymerized chromoionophores were fabricated under mild conditions with an in-house sonic microparticle generator for the measurement of sodium activities at physiological pH. The measuring range for sodium was found as 10 −1–10 −4 M and 1–10 −3 M, for Nile Blue derivatives linked via urea and amide functionalities, respectively, at physiological pH. The observed ion-exchange constants of the plasticizer-free microsphere were log K exch = −5.6 and log K exch = −6.5 for the same two systems, respectively. Compared with earlier Na +-selective bulk optodes, the fabricated optical sensing microbeads reported here have agreeable selectivity patterns, reasonably fast response times, and more appropriate measuring ranges for determination of Na + activity at physiological pH in undiluted blood samples.

Multicolor Quantum Dot Encoding for Polymeric Particle-Based Optical Ion Sensors

Multicolor quantum dot-encoded polymeric microspheres are prepared with controllable and uniform doping levels that function as chemical sensors on the basis of bulk optode theory. TOP/TOPO-capped CdSe quantum dots and CdTe quantum dots capped with CdS (lambdaem = 610 and 700 nm, lambdaex = 510 nm) are blended with a THF solution of poly(methyl methacrylate-co-decyl methacrylate), poly(n-butylacrylate), or poly(vinyl chloride) plasticized with bis(2-ethylhexyl) sebacate without a need for ligand exchange. Polymeric microspheres are generated under mild, nonreactive conditions with a particle caster that breaks down a polymer stream containing the quantum dots into fine droplets by the vibration of a piezocrystal. The resulting microspheres exhibit uniform size and fluorescence emission intensities. Fluorescent bar codes are obtained by subsequent doping of two quantum dots with different colors and mass ratios into the microspheres. A linear relationship is found between the readout fluorescence ratio of the two types of nanocrystals and the mixing ratio. Quantum dot-encoded ion sensing optode microspheres are prepared by simultaneous doping of sodium ionophore X, chromoionophore II, a lipophilic tetraphenylborate cation exchanger, and TOPO-capped CdSe/CdS quantum dot as the fluorescent label. A net positive charge of the quantum dots is found to induce an anion-exchange effect on the sensor function, and therefore, an increased concentration of the lipophilic cation exchanger is required to achieve proper ion sensing properties. The modified quantum dot-labeled sodium sensing microspheres show satisfactory sodium response between 10(-4) and 0.1 M at pH 4.8, with excellent selectivity toward common interferences. The amount of the carried positive charges of the CdSe quantum dots is estimated as 2.8 mumol/g of quantum dots used in this study.

New hexamethine–hemicyanine dyes for the development of integrated optochemical sensors

New far-visible absorbing anilino-cyanine dyes have been synthesised for future application as chromoionophores in integrated waveguide absorbance optodes based on bulk optodes. The effect of the heterocycle, of the substitution of the heterocyclic nitrogen and of the type of heptamethine central ring on the pKa values (4.3-8.2 in ethanol-water solutions and 9.5-11.0 in plasticised PVC membranes), on the spectroscopic characteristics of the dye and on photostability is discussed. pH-selective bulk optodes have been formulated as a first approach to develop ion-selective optodes, and sensitivity, repeatability, lifetime and response time have been determined. The dyes show good analytical behaviour for use as chromoionophores for the development of ion-selective optodes. Reversible (80-87%), fast (tr90%=0.94-2.28 min) and pH-sensitive membranes (slopes of 0.09-0.23 DeltaAbs.pHdec-1, absorbance range 0.19-0.53) have been obtained. Moreover, they exhibit good spectroscopic features for employment with integrated optochemical sensors: absorption maxima of the acidic species in plasticised PVC membranes matched those of 650-670-nm LEDs, high molar absorption coefficients (epsilonacidic=3.5x10(4)-9.3x10(4) L mol-1 cm-1 and epsilonbasic=1.9x10(4)-6.7x10(4) L mol-1 cm-1) and fluorescence.

Flow-through Bulk Optode for Spectrophotometric Determination of Thiocyanate and Its Application to Water and Saliva Analysis

A flow-through spectrophotometric bulk optode for the flow-injectiondetermination of thiocyanate is described. As active constituents, the optode incorporatesthe lipophilized pH indicator 5-octadecanoyloxy-2-(4-nitrophenylazo)phenol andmethyltridodecyl ammonium chloride, dissolved in a plasticized poly(vinyl)chloridemembrane entrapped in a cellulose support. The optode is applied, in conjunction with theflow injection technique, to the determination of thiocyanate at pH 7.5 (TRIS/H2SO4). Thesensor is readily regenerated with a 10-2 M NaOH carrier solution. The analyticalcharacteristics of this optode with respect to thiocyanate response time, dynamicmeasurement range, reproducibility and selectivity are discussed. The proposed FI methodis applied to the determination of thiocyanate in waters from different sources and in humansaliva samples in order to distinguish between smokers and non-smokers.

Nortricarbocyanine dyes as suitable long wavelength pH indicators for chemical sensing

New norcyanine dyes were characterised for their use as long wavelength chromoionophores in optodes. Different membrane compositions were formulated for pH determination in water and their response in terms of sensitivity, linear range, response time and reversibility was examined with the aim to apply them in planar optochemical sensors. Their absorbance maxima are located in the NIR region (785–830 nm), which is very appropriate for applications using common low cost telecommunication components. The characterised optodes showed good analytical features. Hence, fully reversible, reproducible, fast, and sensitive bulk optodes were obtained. The photostability of dyes in the plasticised matrices and their tendency to leach from the membrane phase were also evaluated at different conditions.

Logit linearization of analytical response curves in optical disposable sensors based on coextraction for monovalent anions

The application of a decimal logistic transformation to the sigmoidal calibration curve of ion-selective bulk optodes for the determination of anions based on hydrophobic membranes containing neutral ionophore and chromoionophore is formally established and, consequently, a wide linear calibration function is obtained. The problems derived from the use of a sigmoidal curve in the calibration are therefore solved and the linear dynamic range is increased. The general equation resulting from the logistic transformation is discussed considering the stoichiometric factors for monovalent anions, and the linearization of the theoretical fit to experimental data was checked for two real cases. The strategy was applied to the determination of chloride and nitrate using disposable sensors for different types of waters (tap, well, stream, rain, snow and sea), validating the results against a reference procedure. This new linear calibration proposed for anion determination increases the linear dynamic range up to six orders of magnitude. The main advantage is that it is possible to directly quantify samples with very different analyte contents in a fast and simple way. The methods are easy to use and eliminate the need for prior treatment of the sample.

Establishment of wide-range linear response curves in bulk optode sensors for cations based on ion exchange

A linear curve is obtained when a decimal logistic transformation is applied to the sigmoidal calibration curve of ion-selective bulk optodes for the determination of cations based on ionophore–chromoionophore chemistry. In this way, problems derived from the use of a sigmoidal shape calibration functions are solved and the linear dynamic range is increased. The method is easier to use and eliminates the need for prior treatment of the sample. The influence of different parameters on the linearization of the theoretical model was studied: charge of the analyte, ionophore:chromoionophore ratio and complex stoichiometry, and the goodness of the linearization of the theoretical fit to experimental data for two experimental systems was checked. The procedure was applied to the determination of potassium and hardness using disposable sensors in different types of waters (tap, well, stream, rain, snow and sea), validating the results against a reference procedure. This new linear calibration proposed for cation determination increases the linear dynamic range up to 7–8 orders of magnitude. The main advantage is that it is possible to directly quantify samples with very different analyte contents in a fast and simple way.

RETRACTED: Copper(II)-selective fluorimetric bulk optode membrane based on a 1-hydroxy-9,10-anthraquinone derivative having two propenyl arms as a neutral fluorogenic ionophore

A new optical chemical sensor has been developed for the selective determination of copper(II) ions in aqueous solutions. The reversible sensing system was prepared by incorporating 1-hydroxy-2-(prop-2'-enyl)-4-(prop-2'-enyloxy)-9,10-anthraquinone (AQ) as a neutral Cu2+-selective fluoroionophore in the plasticized PVC membrane with potassium tetrakis(p-chlorophenyl borate) as an anionic additive. The response of the sensor is based on the fluorescence quenching of AQ by Cu2+ ions. At a pH 5.5, the proposed sensor displays a calibration response for Cu2+ over a wide concentration range of 1.0 x 10(-2) to 1.0 x 10(-6) M, with a relatively fast response of less than 40 s. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Cu2+ ion with respect to common co-existing cations. The proposed fluorescence optode was applied successfully to the determination of copper(II) in black tea samples.

Copper(II)-selective fluorimetric bulk optode membrane based on a 1-hydroxy-9,10-anthraquinone derivative having two propenyl arms as a neutral fluorogenic ionophore

A new optical chemical sensor has been developed for the selective determination of copper(II) ions in aqueous solutions. The reversible sensing system was prepared by incorporating 1-hydrpxy-2-(prop-2′-enyl)-4-(prop-2′-enyloxy)-9,10-anthraquinone (AQ) as a neutral Cu2+-selective fluoroionophore in the plasticized PVC membrane with potassium tetrakis(p-chlorophenyl borate) as an anionic additive. The response of the sensor is based on the fluorescence quenching of AQ by Cu2+ ions. At a pH 5.5, the proposed sensor displays a calibration response for Cu2+ over a wide concentration rang of 1.0×10−2 to 1.0×10−6M, with a relatively fast response of less than 40 s. In addition to high stability and reproducibility, the sensor shows a unique selectivity towards Cu2+ ion with respect to common co-existing cations. The proposed fluorescence optode was applied successfully to the determination of copper(II) in black tea samples.

Linear and nonlinear approaches to study transient signals of a flow-through bulk optode

The transient signals obtained with an anion flow-through bulk optode based on a lipophilized pH indicator dissolved in a plasticized poly(vinyl)chloride membrane and entrapped in a cellulose support in response to different concentrations of NO 3 −, Br −, I −, BF 4 −, ClO 4 − and PF 6 − were studied using a flow injection system. The transient signals presented different shapes for each anion. The signal shapes were characterized by means of appropriate parameters, and were found to be dependent on the size and concentration of the anion, providing information that could be used for their identification and quantification. A characteristic portion of the signal was also studied using nonlinear analysis. The results show the existence of chaos and the K 2- entropy (an approximation for the Kolgomorov K-entropy) was seen to be dependent on the size and concentration of anion.

New ketocyanine-based fluorescent optodes for the development of integrated waveguide sensors

Twenty ketocyanine dyes are evaluated as potential pH fluoroionophores to be used in the development of new integrated waveguide fluorescence optodes (IWFOs). Its fluorescence characterization, as well as the pH response is first undertaken in ethanolic solution and then in plasticized PVC membranes with a conventional spectrofluorimeter. Analytical parameters such as basicity, reversibility, leaching and calibration curves are determined in both media and finally, photostability is also measured. Besides, some photophysical fluorescent parameters, such as the emission wavelength, are evaluated for both species, the acidic and the basic form, and quantum yields are calculated in ethanolic solution. Ketocyanine dyes have demonstrated their suitability for being used as acidochromic fluoroionophores in bulk optodes for the development of new IWFOs. They exhibit high fluorescence intensities in the far-visible region, an adequate photostability and an optimum pH response.

Development of a PVC-membrane ion-selective bulk optode, for UO22+ ion, based on tri-n-octylphosphine oxide and dibenzoylmethane

A novel uranyl ion-selective bulk optode membrane, incorporating tri-n-octylphosphine oxide for cation recognition and a lipophilic chromoionophore dibenzoylmethane, has been prepared. The PVC membrane composition was optimized to result in the widest working concentration range. The response range of the proposed optode is 4.1 x 10(-6) to 2.0 x 10(-4) mol L(-1) UO2(2+). The probe works at pH 4.0. Ion interference is low and selectivity, reproducibility, and stability are good.